Adhesive composition for polarizing plate, polarizing plate using same, preparation method therefor, and optical member comprising same

ABSTRACT

Disclosed are an adhesive composition for polarizing plates, a polarizing plate using the same, a method for preparing the same, and an optical member including the same. The adhesive composition includes (A) a (meth)acrylic radical compound, (B) a cationic epoxy compound, (C) a phenoxy resin, and (D) a photoinitiator.

FIELD OF THE INVENTION

The present invention relates to an adhesive composition for polarizing plates, a polarizing plate using the same, a method for preparing the same, and an optical member including the same.

DESCRIPTION OF THE RELATED ART

Adhesives for polarizing plates are used to attach a protective film to one or both sides of a polarizer including a PVA film. As such adhesives for polarizing plates, hydrophilic and water-soluble aqueous PVA adhesives are widely used in the art. However, a polarizing plate prepared using aqueous adhesives may suffer dimensional change due to heat from a backlight, casing localized screen distortion. As a result, partial light leakage can become significant in the case of allowing the overall screen to be displayed in a black state. Thus, the use of a cation polymerizable UV curing adhesive is proposed instead of the aqueous adhesives (For example, Japanese Patent Publication No. 2008-233874A, and the like).

However, since the cation polymerizable UV curing adhesive entails dark reaction (post-polymerization) after UV irradiation, a cured product of the adhesive can be easily wound during storage when prepared in the form of a wound roll. Moreover, the cation polymerizable UV curing adhesive is vulnerable to moisture in the course of curing, thereby making it difficult to maintain curing consistency. Thus, in order to obtain a uniformly cured state, it is necessary to strictly control not only surrounding moisture, but also the content of moisture in a PVA-based polarizer.

To fulfill operating conditions of the polarizing plate, there is a need for a polarizing plate that has better wet-heat resistance than typical polarizing plates in the art and includes an adhesive layer providing strong adhesion and high reliability, and outstanding cohesion, durability and waterproofing.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, an adhesive composition for polarizing plates may include: (A) a (meth)acrylic radical compound, (B) a cationic epoxy compound, (C) a phenoxy resin, and (D) a photoinitiator.

In accordance with another aspect of the invention, a method for preparing an adhesive composition for polarizing plates may include: mixing a (meth)acrylic radical compound, a cationic epoxy compound and a photoinitiator, and adding a phenoxy resin to the mixture.

In accordance with a further aspect of the invention, a polarizing plate may include a polarizer and a protective film stacked on one or both sides of the polarizer via an adhesive layer, wherein the polarizer has a maximum shrinkage length of about 2 mm or less at one end thereof when the polarizing plate is dipped in water having constant temperature of 60° C. for 2 hours.

In accordance with yet another aspect of the invention, an optical member may include the adhesive layer or the polarizing plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a polarizing plate in accordance with one embodiment of the present invention.

FIG. 2 is a sectional view of an optical member in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the terms “upper” and “lower” are defined with reference to the drawings and may also be interpreted as ‘lower’ and ‘upper’ according to orientations, respectively.

In accordance with one aspect of the invention, an adhesive composition for polarizing plates may include (A) a (meth)acrylic radical compound, (B) a cationic epoxy compound, (C) a phenoxy resin, and (D) a photoinitiator.

Herein, the term “compound” includes monomers, oligomers, resins, and the like.

(Meth)Acrylic Radical Compound

The (meth)acrylic radical compound may exhibit high reactivity without suffering reaction interference by moisture of a polarizer. Further, the (meth)acrylic radical compound may improve adhesion with respect to an interface with the polarizer or a protective film during curing and may create a chain transfer bond by including a hydrophilic group with an activated cationic epoxy compound.

The (meth)acrylic radical compound may include a (meth)acrylic compound having at least one hydrophilic group. The hydrophilic group may include at least one of a hydroxyl group and a carboxylic acid group. Preferably, the hydrophilic group may be a hydroxyl group.

The (meth)acrylic radical compound may be a monofunctional (meth)acrylic radical compound rather than polyfunctional (meth)acrylic radical compounds in view of structural flexibility of adhesive layer for polarizing plate.

The (meth)acrylic radical compound may include at least one selected from among (meth)acrylates containing C₁-C₂₀ alkyl group having at least one hydrophilic group, (meth)acrylates containing C₃-C₂₀ alicyclic group having at least one hydrophilic group, and (meth)acrylates containing C₆-C₂₀ aryl group having at least one hydrophilic group.

In some embodiments, the (meth)acrylic radical compound may include at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, 1-chloro-2-hydroxypropyl (meth)acrylate, diethylene glycol mono (meth)acrylate, 1,6-hexanediol mono(meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, 4-hydroxycyclopentyl (meth)acrylate, 2-hydroxy-3-phenyloxybutyl (meth)acrylate, and 4-hydroxycyclohexyl (meth)acrylate, without being limited thereto.

The (meth)acrylic radical compound may be present in an amount of about 1 part by weight to 86 parts by weight based on 100 parts by weight of (A)+(B)+(C). Within this range, the composition can prevent deterioration in adhesion due to reduction of cohesion, deterioration in reliability due to not generating tack by reduction of modulus, and can provide good water resistance by preventing decolorization of the polarizer when dipped in warm water. The (meth)acrylic radical compound is preferably present in an amount of about 10 parts by weight to about 77.5 parts by weight, more preferably about 10 parts by weight to about 57 parts by weight, still more preferably about 19.85 parts by weight to about 49.85 parts by weight.

Cationic Epoxy Compound

The cationic epoxy compound imparts adhesion between the polarizer and the protective film while providing high reliability based on inherent stiffness of an epoxy. Further, the cationic epoxy compound may provide cohesion by entanglement of molecular chains with the (meth)acrylic radical compound and chain transfer coupling with the hydrophilic group of the (meth)acrylic radical compound.

The cationic epoxy compound may be an alicyclic epoxy compound, an aromatic epoxy compound, an aliphatic epoxy compound, a hydrogenated epoxy compound, or mixtures thereof.

The alicyclic epoxy compound may be a compound having at least one epoxy group at an alicyclic ring. The alicyclic epoxy compound may be an alicyclic diepoxy carboxylate. Examples of the alicyclic epoxy compound may include 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane, bis(3,4-epoxycyclohexylmethyl)adipate, bis((3,4-epoxy-6-methylcyclohexyl)methyl)adipate, 3,4-epoxy-6-methylcyclohexyl-3′,4′-epoxy-6′-methylcyclohexane carboxylate, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate, trimethylcaprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate, β-methyl-δ-valerolactone-modified 3,4-epoxycyclohexylmethyl-3′4,′-epoxycyclohexane carboxylate, methylenebis(3,4-epoxycyclohexane), di(3,4-epoxycyclohexylmethyl)ether of ethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate), dioctyl epoxycyclohexahydro phthalate, di-2-ethylhexyl epoxycyclohexahydro phthalate, and the like.

Examples of the aromatic epoxy compound may include bisphenol A, F, and phenol novolac, cresol novolac, bisphenol A-novolac, dichloropentadien novolac, glycidyl ether of triphenolmethane, triglycidyl-p-aminophenol, tetraglycidyl methylenedianiline, and the like.

Examples of the aliphatic epoxy compound may include 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, glycerin triglycidyl ether, polypropylene glycol diglycidyl ethers; polyglycidyl ethers of polyether polyol obtained by adding one or more kinds of alkylene oxide to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, and the like; diglycidyl esters of aliphatic long-chain dibasic acids; monoglycidyl ethers of aliphatic higher alcohols; glycidyl ethers of higher fatty acids; epoxidated soybean oil; butyl epoxystearate; octyl epoxystearate; epoxidated linseed oil; epoxidated polybutadiene, and the like.

The hydrogenated epoxy compound refers to a resin obtained through selective hydrogenation of an aromatic epoxy compound in the presence of a catalyst under pressure. Examples of the aromatic epoxy compound may include bisphenol type epoxy resins such as diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol S, and the like; novolac type epoxy resins, such as a phenol novolac epoxy resin, a cresol novolac epoxy resin, a hydroxybenzaldehyde phenol novolac epoxy resin, and the like; polyfunctional epoxy resins, such as a glycidyl ether of tetrahydroxy phenylmethane, a glycidyl ether of tetrahydroxy benzophenone, epoxidized polyvinylphenol, and the like. Although the hydrogenated epoxy resin can be obtained by adding hydrogen into a mother nucleus of the aromatic epoxy resin, a glycidyl ether of hydrogenated bisphenol A is preferred.

The cationic epoxy compound may be present in an amount of about 10 parts by weight to about 95 parts by weight based on 100 parts by weight of (A)+(B)+(C). Within this range of the cationic epoxy compound, the composition can provide high adhesion between the polarizer and the protective film, does not suffer excessive increase in viscosity and deterioration in cuttability due to brittleness by providing high modulus. The cationic epoxy compound is preferably present in an amount of about 20 parts by weight to about 87.5 parts by weight, more preferably about 40 parts by weight to about 90 part by weight, still more preferably about 50 parts by weight to about 80 part by weight.

The (meth)acrylic radical compound and the cationic epoxy compound may be present in a weight ratio (A):(B) of about 10:90 to about 50:50 based on 100 parts by weight of (A)+(B). With this weight ratio range, the composition can provide desired adhesion between the polarizer and the protective film, and high reliability.

Preferably, based on 100 wt % of the (meth)acrylic radical compound and the cationic epoxy compound, the (A) (meth)acrylic radical compound is present in an amount of about 0.01 wt % to about 59 wt % and the (B) cationic epoxy compound is present in an amount of about 41 wt % to about 99.99 wt %. Within this weight ratio range, the composition can provide desired adhesion between the polarizer and the protective film, and high reliability.

Phenoxy Resin

The phenoxy resin is added to the (meth)acrylic radical compound and the cationic epoxy compound to improve physical cohesion of a cured structure. That is, in the adhesive composition according to the invention, the (meth)acrylic radical compound may be cured by a photoinitiator, particularly, a photo radical polymerization initiator, the cationic epoxy compound may be cured by another photoinitiator, particularly, a photo cationic polymerization initiator, and the phenoxy resin may improve cohesion between cured products from (meth)acrylic radical compound and cationic epoxy compound by providing entanglement thereto.

The phenoxy resin is generally included in the adhesive composition by being dissolved in a solvent. However, since the (meth)acrylic radical compound and the cationic epoxy compound serve as solvents for the phenoxy resin, the adhesive composition of the invention is a solvent-free type composition.

The phenoxy resin may have a softening point of about 0° C. to about 200° C. (preferably in the range of about 100° C. to about 200° C.), a glass transition temperature (Tg) of about 0° C. to 200° C. (preferably in the range of about 50° C. to 100° C.), a weight average molecular weight of about 100 g/mol to about 2,000,000 g/mol (preferably in the range of about 30,000 g/mol to about 60,000 g/mol). Within this range of the phenoxy resin, the composition exhibits improved adhesion and reliability through improvement of cross-linking and cohesion.

Any of non-curable phenoxy resin may be used without limitation so long as the phenoxy resin does not exhibit curing reaction or is not cured by a photoinitiator described below.

In some embodiments, the phenoxy resin may include a resin compound represented by Formula 1:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are the same or different and each is independently hydrogen, a halogen, a C₁-C₁₀ alkyl group, a C₆-C₂₀ aryl group, a C₅-C₂₀ cycloalkyl group or a nitro group; R₉, R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ are the same or different and each is independently hydrogen or a hydroxyl group, at least one of R₉, R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ is a hydroxyl group; X₁ is a single bond, C₁-C₅ linear or branched alkylene group; Z is a hydroxyl group or an epoxy group; and n is an integer from 30 to 400.

In some embodiments, the phenoxy resin may have a repeated structure of bisphenol A.

The phenoxy resin may be present in an amount of about 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of (A)+(B)+(C). Within this range of the phenoxy resin, the adhesive composition does not suffer from deterioration in coatability due to excessive increase in viscosity. The phenoxy resin is preferably present in an amount of about 0.1 parts by weight to about 3 parts by weight, more preferably about 0.15 parts by weight to about 2.5 parts by weight.

Photoinitiator

The composition for adhesives may be a photocurable composition.

The photoinitiator may include a photo-radical polymerization initiator, a photo-cationic polymerization initiator, or combinations thereof.

The photoinitiator may be present in an amount of about 0.1 to about 10 parts by weight based on 100 parts by weight of (A)+(B)+(C). More preferably, the photoinitiator is present in an amount of about 0.1 parts by weight to about 2.5 parts by weight.

The photo-radical polymerization initiator may include typical photo-radical polymerization initiators capable of carrying out photocuring reaction without limitation. For example, the photo-radical polymerization initiator may include phosphorus, triazine, acetophenone, benzophenone, thioxanthone, benzoin, oxime initiators, or mixtures thereof. In one embodiment, the photo-radical polymerization initiator may be bisbenzoylphenyl phosphine oxide, benzoyldiphenyl phosphine oxide, or mixtures thereof.

The photo-radical polymerization initiator may be present in an amount of about 0.1 parts by weight to about 6 parts by weight based on 100 parts by weight of (A)+(B)+(C). Within this range of the photo-radical polymerization initiator, sufficient polymerization of the (meth)acrylic radical compound can be achieved while preventing the initiator from remaining in the composition. The photo-radical polymerization initiator is preferably present in an amount of about 0.1 parts by weight to about 1 part by weight.

Any typical photo-cationic polymerization initiator capable of carrying out photocuring reaction may be used as the photo-cationic polymerization initiator.

For example, the photo-cationic polymerization initiator may include onium salt compounds generating cation species and comprising cation species and anion species. Specific examples of cation species for onium salt compounds may include diaryliodonium, such as diphenyliodonium, 4-methoxydiphenyliodonium, bis(4-methylphenyl)iodonium, bis(4-tert-butylphenyl)iodonium, bis(dodecylphenyl)iodonium, and the like; triarylsulfonium such as triphenyl sulfonium, diphenyl-4-thiophenoxyphenylsulfonium; bis(4-(diphenylsulfonio)phenyl)sulfide, bis[4-(di(4-(2-hydroxyethyl)phenyl)sulfonio)-phenyl]sulfide, 5-2,4-(cyclopentadienyl) [1,2,3,4,5,6-η]-(methylethyl)-benzene]-iron(1+), and the like.

Specific examples of anion species for onium salt compounds may include tetrafluoroborate (BF₄ ⁻), hexafluorophosphate (PF₆ ⁻), hexafluoroantimonate (SbF₆ ⁻), hexafluoroarsenate (AsF₆ ⁻), hexachloroantimonate (SbCl₆ ⁻), and the like.

The photo-cationic polymerization initiator may be present in an amount of about 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of (A)+(B)+(C). Within this range, sufficient polymerization of the cationic epoxy compound can be achieved while preventing the initiator from remaining in the composition. The photo-cationic polymerization initiator is preferably present in an amount of about 0.1 parts by weight to 3 parts by weight.

The adhesive composition may be prepared by mixing the (meth)acrylic radical compound, the cationic epoxy compound, and the photoinitiator, followed by adding the phenoxy resin to the mixture.

The adhesive composition may further include antioxidants, UV absorbents, ionic conductors, additives for conductivity such as conductive metal oxide particles, additives for light spreading properties, viscosity adjustors, and the like in amounts not deteriorating effects of the present invention.

With the components as described above, the adhesive composition may have a viscosity at 25° C. of less than about 150 cPs. Within this viscosity range, the adhesive composition can exhibit good coatability. The adhesive composition preferably has a viscosity from about 1 cPs to about 135 cPs, more preferably from about 40 cPs to about 135 cPs.

The composition may include about 9 wt % to about 57 wt %, preferably about 10 wt % to about 57 wt %, more preferably about 19 to 50 wt % of the (meth)acrylic radical compound; about 40 wt % to about 90 wt %, preferably about 48 wt % to about 80 wt % of the cationic epoxy compound; about 0.1 wt % to 3 wt % of the phenoxy resin; and about 0.1 wt % to about 3 wt % of the photoinitiator in terms of solid content.

In accordance with another aspect of the invention, a polarizing plate may include an adhesive layer formed of the adhesive composition of the invention. FIG. 1 is a sectional view of a polarizing plate according to one embodiment. Referring to FIG. 1, a polarizing plate 100 may include a polarizer 10, a first protective film 20 formed on an upper side of the polarizer 10, and a second protective film 30 formed on a lower side of the polarizer 10, wherein a first adhesive layer 40 is formed between the first protective film 20 and the polarizer 10 and a second adhesive layer 50 is formed between the polarizer 10 and the second protective film 30.

At least one of the first and second adhesive layers 40, 50 may be formed of the adhesive composition for polarizing plates of the present invention.

In FIG. 1, the adhesive layers formed of the adhesive composition according to the embodiment of the invention are respectively formed on both sides of the polarizer. However, it should be understood that the adhesive layer formed of the adhesive composition may be formed on one or both sides of the polarizer. The adhesive layers formed on both sides of the polarizer may be the same or different.

The polarizer may be prepared from a film of a polyvinyl alcohol resin. Examples of the polyvinyl alcohol resin may include saponified products of polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, ethylene acetate vinyl copolymer, and the like. A film formed of a polyvinyl alcohol resin may have a degree of saponification of about 99 mol % or more, preferably from about 99 mol % to about 99.5 mol %, a degree of polymerization of about 2000 or more, preferably from about 2000 to about 2500, and a thickness from about 10 μm to about 200 μm.

The polarizer may be prepared by dyeing a polyvinyl alcohol resin film with iodine and stretching the polyvinyl alcohol resin film. The film may be stretched in a ratio of about 2.0 to about 6.0. After stretching, the film may be subjected to color correction by through dipping in a boric acid solution and an aqueous potassium iodide solution.

The protective film is stacked on one or both sides of the polarizer and any transparent film suitable for use as a polarizing plate may be used as the protective film without limitation. The protective film may be prepared from a material selected from the group consisting of celluloses including triacetyl cellulose (TAC), polyesters including polyethylene terephthalate polyethylene (PET), cyclo-polyolefins (COP), polycarbonates (PC), polyacrylates, polyethersulfones, polysulfones, polyamides, polyimides, polyolefins, polyarylates, polyvinyl alcohols, polyvinyl chlorides, polyvinylidene chlorides, and mixtures thereof.

The protective film may have a thickness from about 25 μm to about 500 μm. Within this thickness range, the protective film can be applied to the polarizing plate. Preferably, the protective film has a thickness of about 25 μm to about 100 μm.

The protective film may be subjected to surface treatment, for example, corona pretreatment at about 250 mJ/cm² or more, before application of the adhesive composition or before preparation of the polarizing plate.

The polarizing plate may be prepared by any typical method. In some embodiments, a protective film having an adhesive composition layer is prepared by depositing the adhesive composition on one side of the protective film. As needed, the adhesive composition layer may be subjected to drying and the like. The adhesive composition may be coated by, for example, die coating, roll coating, gravure coating, spin coating, and the like on the protective film. Then, a stack product is prepared by stacking the protective film having the adhesive composition layer on each of upper and lower surfaces of a polarizer while the adhesive composition layer is contacted with the polarizer. The adhesive composition layer is cured by UV irradiation to form an adhesive layer, thus form a polarizing plate

Although the intensity of UV irradiation is not particularly limited, UV irradiation is performed at a wavelength of about 200 nm to about 450 nm and an intensity of illumination of about 1 mW/cm² to about 500 mW/cm² to have a UV irradiation dose of about 10 mJ/cm² to about 10,000 mJ/cm². UV irradiation may be performed using a metal halide lamp or the like. UV irradiation may be performed at a temperature of about 22° C. to about 25° C. and a relative humidity of about 20% to about 60%.

The polarizing plate according to the invention has high cohesion, durability and cross-linking density, thereby providing high adhesion/reliability.

In some embodiments, when the polarizing plate is dipped in water having a constant temperature of 60° C. for 2 hours, the polarizer may have a maximum shrinkage length of about 2 mm or less at one end thereof, preferably about 0.1 mm to about 2 mm, more preferably about 0.1 mm to about 1.7 mm, and still more preferably about 0.3 mm to about 1.0 mm. In this case, the polarizing plate has a size of 5 cm×5 cm (length×width), and an adhesive layer is stacked to a thickness of 1 μm on either side of a 20 μm thick polarizer, followed by stacking a protective film having a thickness of 30 μm to 80 μm to provide a structure as shown in FIG. 1.

As used herein, the term “shrinkage length” means the shortest distance from one end of the protective film to one end of the polarizer adjacent the one end of the protective film in the polarizing plate after the polarizing plate is dipped in warm water for example water having a constant temperature of 60° C. for 2 hours. The protective film does not shrink even after dipping test in warm water, whereas the polarizer can shrink upon dipping test in warm water. The adhesive layer prepared from the adhesive composition of the present invention may decrease the shrinkage of the polarizer in the dipping of the polarizing plate by interfering of the shrinkage of the polarizer by cohesion.

In accordance with a further aspect of the invention, an optical member may include the adhesive composition for polarizing plates, an adhesive layer formed of the adhesive composition, or a polarizing plate including the same.

The optical member refers to a typical display device including the polarizing plate, and may include a liquid crystal display, an organic light emitting display (OLED), and the like, without being limited thereto.

FIG. 2 is a sectional view of an optical member in accordance with one embodiment of the invention.

Referring to FIG. 2, the optical member may include a display panel 200; and a polarizing plate 110 formed on an upper side of the display panel 200.

Hereinafter, the present invention will be explained in more detail with reference to the following examples and comparative examples. It should be understood that these examples are provided for illustration only and are not to be in any way construed as limiting the present invention.

Detailed components of adhesive compositions used in the following examples and comparative examples were as follows.

A. (Meth)acrylic radical compound:

(A1) 2-hydroxyethyl acrylate (2-HEA) (100%, SK Cytec)

(A2) 4-hydroxybutyl acrylate (4-HBA) (100%, Osaka Organic)

B. Cationic epoxy compound:

(B1) Alicyclic diepoxy carboxylate (CY-179, Huntmans)

(B2) Aliphatic epoxy (monofunctional, water-soluble) (EX-216, Nagase)

(B3) Bisphenol A aromatic epoxy (YX8000, JER)

C. Phenoxy resin:

(C1) PKHB (Phenoxy resin, softening temperature: 200° C., Tg: 84° C., Mw: 32,000 g/mol, INCHEM),

(C2) PKHH (Phenoxy resin, softening temperature: 200° C., Tg: 92° C., Mw: 52,000 g/mol, INCHEM)

D. Photoinitiator:

(D1) Photo-radical polymerization initiator: 2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide (Darocure TPO, Ciba)

(D2) Photo-cationic polymerization initiator: triarylsulfonium salt containing PF₆ ⁻ and SbF₆ ⁻ as anionic species (CPI-210S)

E. Alkyl group-containing monomer:

(E1) Ethyl acrylate (100%, Samchum Chemical)

(E2) Butyl acrylate (100%, Samchum Chemical).

Example 1

Without using a solvent, 49.85 parts by weight of (A1) 2-hydroxyethyl acrylate (2-HEA) as a (meth)acrylic radical compound, 50 part by weight of (B1) alicyclic diepoxy carboxylate (CY-179) as a cationic epoxy compound, 0.5 parts by weight of (D1) a photo-radical polymerization initiator and 2 parts by weight of (D2) a photo-cationic polymerization initiator were mixed. Then, 0.15 parts by weight of (C1) PKHB as a phenoxy resin was added to the mixture, thereby preparing an adhesive composition.

Examples 2 to 9 and Comparative Examples 1 to 8

Adhesive compositions were prepared in the same manner as in Example 1, except that the amounts and kinds of the (meth)acrylic radical compound, cationic epoxy compound, phenoxy resin and photoinitiator were changed as in Table 1 (unit: parts by weight).

TABLE 1 A B C D E A1 A2 B1 B2 B3 C1 C2 D1 D2 E1 E2 Example1 49.85 — 50 — — 0.15 — 0.5 2 — — Example2 39.85 — 60 — — 0.15 — 0.5 2 — — Example3 29.85 — 70 — — 0.15 — 0.5 2 — — Example4 19.85 — 80 — — 0.15 — 0.5 2 — — Example5 47.5 — 50 — — 2.5 — 0.5 2 — — Example6 — 39 60 — — 1 — 0.5 2 — — Example7 39 — 60 — — — 1 0.5 2 — — Example8 39 — — 60 — 1 — 0.5 2 — — Example9 39 — — — 60 1 — 0.5 2 — — Comparative 60 — 40 — — — — 0.5 2 — — Example1 Comparative 59.95 — 40 — — 0.05 — 0.5 2 — — Example2 Comparative 44 — 50 — — 6 — 0.5 2 — — Example3 Comparative — — 40 — — 1 — 0.5 2 59 — Example4 Comparative — — — 40 — 1 — 0.5 2 — 59 Example5 Comparative — 60 — 40 — — — 0.5 2 — — Example6 Comparative 10 — 90 — — — — 0.5 2 — — Example7 Comparative — — 99 — — — 1 0.5 2 — — Example8

Preparation of Polarizing Plate

An 80 μm thick polyvinyl alcohol film (degree of saponification: 99.5 mol %, degree of polymerization: 2000) was used as a base film. The base film was dipped in 0.3% iodine solution for dyeing and was subjected to stretching at a ratio of 5.0 times. Then, the stretched base film was dipped in a boric acid solution at a concentration of 3% and an aqueous solution of 2% potassium iodide for color correction, followed by drying at 50° C. for 4 minutes, thereby preparing a polarizer.

As a first transparent protective film, an 80 μm thick triacetate cellulose (TAC) film was used and subjected to corona treatment at 250 mJ/cm² or more.

As a second transparent protective film, a 30 μm thick cyclo-polyolefin (COP) film was used and subjected to corona treatment at 250 mJ/cm² or more.

A polarizing plate was prepared by combining the first protective film, the adhesive composition, the polarizer, the adhesive composition and the second protective film in this order at 22˜25° C. and 20˜60% RH, followed by UV irradiation at 400 mW/cm² to 1000 mJ/cm² using a metal halide lamp at 22-25° C. and 20˜60% RH.

The prepared adhesive compositions or the polarizing plate were evaluated as to the following properties. Results are shown in Table 2.

-   -   (1) Adhesion: To confirm adhesion of the polarizing plate, a         cutter blade was inserted into a portion between the protective         film and the polarizer at one end of the polarizing plate. No         insertion of the cutter blade between the protective film and         the polarizer was evaluated as ⊚, slight insertion of the cutter         blade was evaluated as ◯, slight insertion of the cutter blade         and tearing of the protective film due to strength thereof was         evaluated as Δ, and easy insertion of the cutter blade was         evaluated as X.

(2) Cuttability: To confirm cuttability of the polarizing plate, each of the polarizing plates having a size of 500 mm×500 mm (length×width) and prepared in the examples and the comparative examples was punched from the protective film (80 μm thick triacetyl cellulose (TAC)) side using a cutter blade. The peeled state of one end at four sides of the punched polarizing plate was visibly observed. No peeling was evaluated as ⊚, peeling to a length of 1 mm or less was evaluated as ◯, peeling to a length of greater than 1 mm to 2 mm or less was evaluated as Δ, and peeling to a length of greater than 2 mm was evaluated as X.

(3) Water resistance (warm water dipping testing): Each of the polarizing plates prepared in the examples and the comparative examples was cut to a size of 5 cm×5 cm (length×width). Each of the prepared polarizing plate was dipped in water having constant temperature of 60° C. for 2 hours. Decoloration of the polarizer and maximum shrinkage length at one end of the polarizer were measured. The shrinkage length means the shortest distance from one end of the protective film to one end of the polarizer adjacent the one end of the protective film in the polarizing plate in the course of warm water dipping test above. Although the protective film did not shrink during water resistance testing, the polarizer shrunk when dipped in warm water. No decoloration of the polarizer was evaluated as ◯ (shrinkage length of 2 mm or less), partial decoloration was evaluated as Δ (shrinkage length of 3 mm or less to more than 2 mm), and complete decoloration was evaluated as X (shrinkage length of more than 3 mm).

(4) Viscosity: The adhesive composition was stored in a pyrostat (25° C.) for 24 hours. After 400 g of the composition was placed in a 500 ml Nalgene bottle (73.8 mm outer diameter×169.8 mm height), the viscosity of the composition was measured using a Brookfield viscometer DV-II+ at 25° C. at 100 rpm with Spindle No. #7.

TABLE 2 Water resistance Polarizer shrinkage Viscosity Polarizer length (25° C., Adhesion Cuttability separation (mm) cPs) Example 1 ⊚ ⊚ ◯ 0.5 40 Example 2 ⊚ ⊚ ◯ 0.3 68 Example 3 ⊚ ◯ ◯ 1.7 103 Example 4 ⊚ ◯ ◯ 1.5 127 Example 5 ⊚ ⊚ ◯ 0.8 75 Example 6 ⊚ ⊚ ◯ 0.7 87 Example 7 ⊚ ⊚ ◯ 1.0 85 Example 8 ◯ ⊚ ◯ 1.5 45 Example 9 ◯ ⊚ ◯ 1.6 135 Comparative Δ ⊚ X 5.5 28 Example 1 Comparative Δ ⊚ X 5.8 30 Example 2 Comparative Δ X Δ 2.4 250 Example 3 Comparative X X X 4.5 29 Example 4 Comparative X X X 3.7 32 Example 5 Comparative X Δ Δ 2.7 27 Example 6 Comparative Δ X X 6.4 235 Example 7 Comparative X X X 6.6 351 Example 8

As shown in Table 2, the polarizing plate including an adhesive layer formed of the adhesive composition according to the invention exhibited good adhesion, cuttability and water resistance, and thus did not suffer separation of the polarizer and had a polarizer shrinkage length of 2 mm or less during warm water dipping testing. In addition, the adhesive composition according to the invention had a viscosity of less than 150 cPs, indicating good coatability.

Those skilled in the art will understand that the present invention is not limited by the aforementioned embodiments and the drawings, and that various modifications, changes, and alterations can be made without departing from the spirit and scope of the invention. Therefore, these embodiments are provided for illustration only and are not to be construed in any way as limiting the present invention. 

1. An adhesive composition for a polarizing plate, the adhesive composition comprising: (A) a (meth)acrylate compound, (B) a cationic epoxy compound, (C) a phenoxy resin, and (D) a photoinitiator.
 2. The adhesive composition according to claim 1, wherein the (C) phenoxy resin is present in an amount of about 0.1 parts by weight to about 5 parts by weight, based on 100 parts by weight of (A)+(B)+(C).
 3. The adhesive composition according to claim 1, wherein the adhesive composition is a solvent-free adhesive composition.
 4. The adhesive composition according to claim 1, wherein a weight ratio of the (A) (meth)acrylate compound: the (B) cationic epoxy compound ranges from about 10:90 to about 50:50.
 5. The adhesive composition according to claim 1, wherein the (C) phenoxy resin includes a non-curable phenoxy resin.
 6. The adhesive composition according to claim 1, wherein the (C) phenoxy resin includes a resin compound represented by Formula 1:

wherein, R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are each independently hydrogen, a halogen, a C₁-C₁₀ alkyl group, a C₆-C₂₀ aryl group, a C₅-C₂₀ cycloalkyl group, or a nitro group; R₉, R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ are each independently hydrogen or a hydroxyl group, at least one of R₉, R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ being a hydroxyl group; X₁ is a single bond or a linear or branched C₁-C₅ alkylene group; Z is a hydroxyl group or an epoxy group; and n is an integer from 30 to
 400. 7. The adhesive composition according to claim 1, wherein the (A) (meth)acrylate compound includes a C₁-C₂₀ alkyl group that has at least one hydrophilic group.
 8. The adhesive composition according to claim 1, wherein the (B) cationic epoxy compound includes an alicyclic epoxy compound, an aromatic epoxy compound, an aliphatic epoxy compound, a hydrogenated epoxy compound, or mixtures thereof.
 9. The adhesive composition according to claim 1, wherein the adhesive composition includes: about 1 part by weight to about 86 parts by weight of the (A) (meth)acrylate compound, about 10 parts by weight to about 95 parts by weight of the (B)cationic epoxy compound, about 0.1 parts by weight to about 5 parts by weight of the (C)phenoxy resin, and about 0.1 parts by weight to about 10 parts by weight of the (D) photoinitiator, all amounts based on 100 parts by weight of (A)+(B)+(C).
 10. The adhesive composition according to claim 1, wherein the adhesive composition has a viscosity at 25° C. of about 40 cPs to about 135 cPs.
 11. A polarizing plate, comprising: a polarizer; and a protective film stacked on one or both sides of the polarizer via an adhesive layer, wherein the polarizer has a maximum shrinkage length of about 2 mm or less at one end thereof when the polarizing plate is dipped in water having a constant temperature of 60° C. for 2 hours.
 12. The polarizing plate according to claim 11, wherein the adhesive layer is prepared from an adhesive composition for polarizing plates, the adhesive composition including: (A) a (meth)acrylate compound, (B) a cationic epoxy compound, (C) a phenoxy resin, and (D) a photoinitiator.
 13. A method for preparing a polarizing plate, the method comprising: depositing the adhesive composition according to claim 1 on one side of a protective film to prepare a protective film having an adhesive composition layer; stacking the protective film having the adhesive composition layer thereon on both an upper side and a lower side of a polarizer; and UV irradiating the adhesive composition layer.
 14. An optical member comprising an adhesive film prepared from the adhesive composition as claimed in claim
 1. 15. An optical member comprising the polarizing plate as claimed in claim
 11. 